Binding of insulin to thymocytes from suckling and hypophysectomized rats: evidence for two mechanisms regulating insulin sensitivity.

Insulin more effectively increased amino acid influx into thymocytes isolated from insulin-sensitive suckling and hypophysectomized rats than into cells obtained from normal adult animals. Thymocytes from hypophysectomized adult rats bound more insulin than did cells from sham-operated controls, suggesting that insulin sensitivity in this condition was due to an increase in the number of insulin receptors. In contrast, thymocytes from suckling rats bound the same amount of insulin as did cells from adult animals, suggesting that in this instance insulin sensitivity was the result of changes in events subsequent to the binding of insulin.